The present invention generally relates to bodily fluid sampling devices and more specifically, but not exclusively, concerns an integrated lancing test strip with a unique retractable lancet.
The acquisition and testing of bodily fluids is useful for many purposes, and continues to grow in importance for use in medical diagnosis and treatment, such as for diabetes, and in other diverse applications. In the medical field, it is desirable for lay operators to perform tests routinely, quickly and reproducibly outside of a laboratory setting, with rapid results and a readout of the resulting test information. Testing can be performed on various bodily fluids, and for certain applications, is particularly related to the testing of blood and/or interstitial fluid. Such fluids can be tested for a variety of characteristics of the fluid, or analytes contained in the fluid, in order to identify a medical condition, determine therapeutic responses, assess the progress of treatment, and the like.
The testing of bodily fluids basically involves the steps of obtaining the fluid sample, transferring the sample to a test device, conducting a test on the fluid sample, and displaying the results. These steps are generally performed by a plurality of separate instruments or devices. Performing these steps can be difficult for patients, especially for patients with limited hand dexterity, such as the elderly, or those suffering the effects of their condition, like diabetes. Diabetics suffer many symptoms that can make self-monitoring difficult. For example, diabetics can sometimes experience numbness or tingling in their extremities, such as their hands, and also, wounds tend to heal more slowly for diabetics. In a typical procedure, the patient first creates an incision in the skin by lancing the skin with a lancet. In order to ensure that a sufficient number of capillaries are cut for supplying an adequate bodily fluid sample, the incision has to usually be deep, which can be rather painful for the patient. Often, the incision still does not provide an adequate amount bodily fluid for the sample, and the patient then must resort to expressing the fluid from the incision. If during expression of the fluid the patient is not careful, smearing of the fluid may occur, which may result in rendering the sample useless. Once a sufficient amount of fluid collects as a droplet on the skin, the patient has to position a test strip over the site such that the test strip contacts and absorbs a sufficient amount of the droplet for testing. Usually the droplet of fluid is quite small, and patients, especially ones with hand motor control problems, may experience great difficulty in positioning the test strip so as to collect a sample from the droplet. As should be appreciated, patients can become frustrated by this procedure, and consequently, they may perform the test less often or may even quit testing altogether.
Recently, integrated lancing test strips have been developed in which a test strip is integrated with a lancet so as to form a single disposable unit. While these integrated units have somewhat simplified the collection and testing of fluid samples, there are still a number of issues that need to be resolved before a commercial unit can be implemented. One issue concerns the interaction between the lancet and the test strip during fluid collection. In one type of design, the lancet is fixed relative to the test strip and extends past the edge of the test strip. During lancing, the entire integrated lancing test strip is fired by a lancing mechanism to form an incision, and after forming the incision, the entire integrated lancing test strip is typically retracted from the skin so that the blade is removed from the incision in order to promote blood flow as well as to dull the pain.
With the lancet fixed relative to the strip, a number of difficulties in sampling the fluid are created. For instance, as noted before, the lancet typically extends from the test strip near the capillary opening for the test strip. At such a position, the blade of the lancet can interfere with the collection of body fluid by smearing the droplet of blood on the skin and/or by drawing blood away from the capillary channel. Further, the distance that the capillary has to be retracted is directly proportional to the length of the lancet blade that extends from the test strip. The greater penetration depth created by longer lancet blades usually increases the amount of blood that is bled from the incision, but the greater length of the lancet necessitates that the test strip be retracted farther away from the skin, which in turn can reduce the chances that the blood will be successfully drawn into the capillary channel of the test strip. Conversely, shorter lancets reduce the distance of the test strip from the skin, but shorter lancets normally produce smaller fluid sample sizes from the incision. Moreover, retraction of the entire integrated device is sometimes inconsistent, thereby leading to some undesirable consequences. If the integrated device is retracted too far from the skin, the capillary channel might not be able to contact the fluid droplet on the skin, thereby resulting in an incomplete test or insufficient sample size for testing.
Some previous integrated disposable designs were proposed in which a lancet is fixed to a body that holds a separate sensor, which is then rotated into position to collect body fluid. However, the body for such type of disposable was typically made from an extruded plastic that made them rather bulky and expensive to manufacture. Due to their bulky nature, these types of disposables were difficult to incorporate into magazines, drums, cassettes, cartridges and the like.
To alleviate some of these difficulties, integrated lancing test strips have been developed in which the lancet is moveable relative to the test strip. However, such designs still have a number of drawbacks. One issue concerns maintaining the sterility of the lancet so as to minimize the risk of infection. In practice, conventional plastic or syringe type caps that are used to maintain the sterility of typical lancets cannot be incorporated with the moveable lancet design for several reasons. With typical syringe type caps, the cap encapsulates the lancet, and the cap is removed by pulling or twisting the cap off the lancet. However, by its moveable nature, the removal of the cap from the lancet without destroying the integrated device is difficult or even practically impossible. For instance, as the cap is pulled, the lancet moves, which in turn prevents the removal of the cap, and if pulled too much, the lancet can become dislodged from the rest of the integrated lancing test strip. Another issue with the moveable lancet design concerns the positioning of the capillary opening in the test strip after lancing. During a normal sampling procedure, the end of the test strip contacts the skin during lancing so as to control the penetration depth of the lancet and remains in contact with the skin as the fluid from the incision is collected. However, the pressure exerted by the test strip against the skin can constrict the fluid flow from the incision such that the fluid sample size might be too small for accurate analysis. Other systems retract the test strip from the skin, but this is prone to creating positional errors such that the capillary channel opening can be located too far away from the skin to collect fluid. In either case, safe disposal of the integrated device is always a concern. Since the lancet is moveable, it can sometimes extend from the test strip after lancing, thereby creating a potential cutting hazard. Springs or other biasing mechanisms can be used to bias the lancet inside the device in an unexposed position, but occasionally, the integrated device can be compressed or jarred so that the lancet is exposed to create a puncture hazard after use.
Thus, needs remain for further contributions in this area of technology.